1. Field of the Disclosure
The present disclosure is related to the field of production logging of oil and gas wells. More specifically, the present disclosure is related to methods of determining volumetric flow rates of gas and liquid in highly inclined wellbores particularly when the flow regime substantially consists of stratified gas-liquid flow.
2. Description of the Related Art
Production logging of oil and gas wells is used to determine, with respect to depth, the flow rates of the various fluids flowing within the wellbore. Production logging includes lowering instruments into the wellbore at one end of an armored electrical cable. The instruments communicate signals along the cable to a recording system at the earth's surface wherein the instrument signals are converted into measurements corresponding to the flow rates of the fluids in the wellbore with respect to depth.
A particularly difficult flow condition to measure in highly inclined wellbores using the production logging tools known in the art is so-called stratified flow, in which the fluids in the wellbore comprise gas and liquid. Gas typically will occupy the upper portion of the wellbore, and the liquid will occupy the lower portion. In order for the wellbore operator to determine the volumetric flow rates of gas and liquid flowing in such a wellbore, the operator must be able to determine gas velocity, liquid velocity and the fractional amount of the wellbore cross-section occupied by each.
U.S. Pat. No. 5,633,470 to Song, having the same assignee as the present disclosure and the contents of which are incorporated herein by reference, teaches a method of determining volumetric flow rates of gas and liquid in an inclined conduit. The method includes measuring the velocity the gas, measuring the velocity of the liquid, calculating a fractional amount of the cross-sectional area of the conduit occupied by the gas and occupied by the liquid, and calculating the volumetric flow rates from the measurements of velocity and from the calculated fractional amounts of the cross-sectional area of the conduit occupied by the gas and by the liquid. In one embodiment, the gas velocity is measured by cross-correlating measurements of two spaced apart temperature sensors after momentarily heating the gas. In one embodiment, the liquid velocity is measured by a spinner flowmeter.
The present disclosure does not require the use of temperature sensors and furthermore eliminates the use of spinner flowmeters that can alter the flow velocity of a fluid. Furthermore, the robustness and novelty of the design relies on the combinatorial implementation of transit time (time of flight) and cross-correlation (finite eddy/impedance detection) using acoustic transducer pairs and pairs of pairs of acoustic transducers. Transit time (time of flight) measurements perform well in laminar flow conditions while the cross-correlation method complements the transit time method by excelling in mixed multiphase conditions.